6 s_client - SSL/TLS client program
10 B<openssl> B<s_client>
11 [B<-connect host:port>]
14 [B<-certform DER|PEM>]
18 [B<-CApath directory>]
38 [B<-cipher cipherlist>]
39 [B<-starttls protocol>]
45 The B<s_client> command implements a generic SSL/TLS client which connects
46 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
53 =item B<-connect host:port>
55 This specifies the host and optional port to connect to. If not specified
56 then an attempt is made to connect to the local host on port 4433.
58 =item B<-cert certname>
60 The certificate to use, if one is requested by the server. The default is
61 not to use a certificate.
63 =item B<-certform format>
65 The certificate format to use: DER or PEM. PEM is the default.
69 The private key to use. If not specified then the certificate file will
72 =item B<-keyform format>
74 The private format to use: DER or PEM. PEM is the default.
78 the private key password source. For more information about the format of B<arg>
79 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)|openssl(1)>.
81 =item B<-verify depth>
83 The verify depth to use. This specifies the maximum length of the
84 server certificate chain and turns on server certificate verification.
85 Currently the verify operation continues after errors so all the problems
86 with a certificate chain can be seen. As a side effect the connection
87 will never fail due to a server certificate verify failure.
89 =item B<-CApath directory>
91 The directory to use for server certificate verification. This directory
92 must be in "hash format", see B<verify> for more information. These are
93 also used when building the client certificate chain.
97 A file containing trusted certificates to use during server authentication
98 and to use when attempting to build the client certificate chain.
102 reconnects to the same server 5 times using the same session ID, this can
103 be used as a test that session caching is working.
107 pauses 1 second between each read and write call.
111 display the whole server certificate chain: normally only the server
112 certificate itself is displayed.
116 print session information when the program exits. This will always attempt
117 to print out information even if the connection fails. Normally information
118 will only be printed out once if the connection succeeds. This option is useful
119 because the cipher in use may be renegotiated or the connection may fail
120 because a client certificate is required or is requested only after an
121 attempt is made to access a certain URL. Note: the output produced by this
122 option is not always accurate because a connection might never have been
127 prints out the SSL session states.
131 print extensive debugging information including a hex dump of all traffic.
135 show all protocol messages with hex dump.
139 tests non-blocking I/O
143 turns on non-blocking I/O
147 this option translated a line feed from the terminal into CR+LF as required
152 inhibit shutting down the connection when end of file is reached in the
157 inhibit printing of session and certificate information. This implicitly
158 turns on B<-ign_eof> as well.
160 =item B<-psk_identity identity>
162 Use the PSK identity B<identity> when using a PSK cipher suite.
166 Use the PSK key B<key> when using a PSK cipher suite. The key is
167 given as a hexadecimal number without leading 0x, for example -psk
170 =item B<-ssl2>, B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1>
172 these options disable the use of certain SSL or TLS protocols. By default
173 the initial handshake uses a method which should be compatible with all
174 servers and permit them to use SSL v3, SSL v2 or TLS as appropriate.
176 Unfortunately there are a lot of ancient and broken servers in use which
177 cannot handle this technique and will fail to connect. Some servers only
178 work if TLS is turned off with the B<-no_tls> option others will only
179 support SSL v2 and may need the B<-ssl2> option.
183 there are several known bug in SSL and TLS implementations. Adding this
184 option enables various workarounds.
186 =item B<-cipher cipherlist>
188 this allows the cipher list sent by the client to be modified. Although
189 the server determines which cipher suite is used it should take the first
190 supported cipher in the list sent by the client. See the B<ciphers>
191 command for more information.
193 =item B<-starttls protocol>
195 send the protocol-specific message(s) to switch to TLS for communication.
196 B<protocol> is a keyword for the intended protocol. Currently, the only
197 supported keywords are "smtp" and "pop3".
201 specifying an engine (by it's unique B<id> string) will cause B<s_client>
202 to attempt to obtain a functional reference to the specified engine,
203 thus initialising it if needed. The engine will then be set as the default
204 for all available algorithms.
206 =item B<-rand file(s)>
208 a file or files containing random data used to seed the random number
209 generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>).
210 Multiple files can be specified separated by a OS-dependent character.
211 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
216 =head1 CONNECTED COMMANDS
218 If a connection is established with an SSL server then any data received
219 from the server is displayed and any key presses will be sent to the
220 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
221 have been given), the session will be renegotiated if the line begins with an
222 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
223 connection will be closed down.
227 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
230 openssl s_client -connect servername:443
232 would typically be used (https uses port 443). If the connection succeeds
233 then an HTTP command can be given such as "GET /" to retrieve a web page.
235 If the handshake fails then there are several possible causes, if it is
236 nothing obvious like no client certificate then the B<-bugs>, B<-ssl2>,
237 B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> options can be tried
238 in case it is a buggy server. In particular you should play with these
239 options B<before> submitting a bug report to an OpenSSL mailing list.
241 A frequent problem when attempting to get client certificates working
242 is that a web client complains it has no certificates or gives an empty
243 list to choose from. This is normally because the server is not sending
244 the clients certificate authority in its "acceptable CA list" when it
245 requests a certificate. By using B<s_client> the CA list can be viewed
246 and checked. However some servers only request client authentication
247 after a specific URL is requested. To obtain the list in this case it
248 is necessary to use the B<-prexit> option and send an HTTP request
249 for an appropriate page.
251 If a certificate is specified on the command line using the B<-cert>
252 option it will not be used unless the server specifically requests
253 a client certificate. Therefor merely including a client certificate
254 on the command line is no guarantee that the certificate works.
256 If there are problems verifying a server certificate then the
257 B<-showcerts> option can be used to show the whole chain.
261 Because this program has a lot of options and also because some of
262 the techniques used are rather old, the C source of s_client is rather
263 hard to read and not a model of how things should be done. A typical
264 SSL client program would be much simpler.
266 The B<-verify> option should really exit if the server verification
269 The B<-prexit> option is a bit of a hack. We should really report
270 information whenever a session is renegotiated.
274 L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)>